Many prior art references teach methods for increasing the amount of oil recoverable from a subterranean earth formation containing oil or petroleum by methods described in the art as secondary recovery, tertiary recovery, enhanced recovery, supplemental recovery, etc., all of which share the common feature of employing an injected fluid which displaces oil from the flow channels or the formation, and displaces it toward one or more spaced-apart producing wells. Fluids employed for this process include water, steam, water containing chemical additives including surface active agents or surfactants, as well as viscosity increasing hydrophilic polymers, all of which are known and used for the purpose of increasing the amount of oil recoverable from subterranean formations. All enhanced recovery processes employing a fluid which is injected into one or more wells to displace petroleum toward one or more spaced-apart production wells, have experienced only limited success because of a number of problems which are encountered in applying the process. One serious problem which has been encountered is concerned with the failure of the injected fluid to sweep as large a segment of the formation as is expected. One commonly used pattern called an inverted five spot, comprises an injection well located in the center of a more or less square grid and four production wells surround the injection well, one located at each corner of the square. When water or other oil displacing fluids are injected into the central injection well, oil is displaced only from the portions of the formation swept by the injected fluid which is only about 70% of the total area of the pattern. The failure to sweep all of the area within the square is referred to as poor sweep efficiency or poor horizontal conformance.
Numerous processes have been disclosed in the literature for the purpose of improving the sweep efficiency of a displacement type enhanced oil recovery process. Numerous complex patterns and multi step processes have been disclosed, by means of which the amount of formation swept by the injected fluid is increased, but cost of drilling the additional wells required is frequently excessive in relation to the improvement in sweep efficiency attained. None of these procedures have been entirely satisfactory.
In view of the current shortage of petroleum products, there is a substantial need for a method which will improve the sweep efficiency of displacement type enhanced oil recovery processes without requiring the drilling of additional wells above those normally employed in conventional enhanced oil recovery techniques.